Like I said part is physical size, that Kontronik motor is equivalent in size to a Speed 400 (400s are actually around 40mm long not nearly 16 inches !). The last part for Kontronik is not the number of turns of wire in the motor, which is more common, it's the Kv (revs/Volt) divided by 100. The higher the number the "hotter" the motor, i.e. the more revs it produces for a given voltage.

(Edited cus I got it the wrong way round first time)

Steve